There are known power presses comprising a flywheel for accumulating kinetic energy in the interval between two blows. On the shaft of this flywheel there is disposed the driving component of a single-revolution clutch, while the driven component of the single-revolution clutch and a brake are fixed to a working shaft. This working shaft is connected to a slide by means of an excentric, a cam or a crank mechanism.
It is a drawback of these presses, that only a part of the energy accumulated by the flywheel is utilized. This energy acts on the workpiece for a very short time within the duration of the cycle in the form of blows; this results in a poor quality of the worked surfaces, while the process of plastic deformation is accompanied by high noise and vibrations. The poor quality of the stamping arises because the sheared surface is only partially smooth, while its greater part is broken and rough, and in the case of sheet material shaping, the material is thinned and even torn.
A further drawback is that, when the working shaft is connected to the slide by means of an excentric or a crank mechanism, the maximum force is obtained at the end of the stroke. This creates a constant danger of jamming of the press and requires a greater spreading of the tools than might otherwise be required by the process, thereby causing an intensive wear as a result of friction and heating, an impaired guiding of the movable parts of the tools, wearing out of their working edges, an increase of their cost and a limitation of the speed and productivity. When the working shaft is connected to the slide by means of a cam mechanism, the press is not versatile, i.e. is suitable only for the working of workpieces for which the cam is profiled and then only with small forces.
Another drawback lies in the need for the flywheel, a single-revolution clutch and a brake, which results in an increase of overall size, weight and price of the presses. Since the single-revolution clutch and the brake are fixed to the shaft which transmits the maximum torque, there is a danger of frequency failures, spontaneous engagements etc.
There are also known other types of presses, e.g. hydraulic presses, which compared with power presses of corresponding forces are much more expensive, of lower speed, of more complex design, comprises increasingly complex units and require a much better maintenance, particularly because of leakage through the seals.